1. Field
The present disclosure relates generally to shims and, in particular, to predicting the shapes of required shims. Still more particularly, the present disclosure relates to a method and apparatus for predicting the shapes of shims needed for filling in the space between a rigid surface and a flexible surface that have been mated.
2. Background
Various surfaces may be mated when components are attached or assembled together during the manufacturing of an object. In some cases, one or more gaps may be present between the mated surfaces. These gaps may affect the performance, aesthetic, or some other aspect of the object in an undesired manner. Thus, it may be desirable to substantially fill these gaps using, for example, shims. A shim typically takes the form of a solid member that is made of metal, plastic, a composite material, or some other type of material. The process of filling these gaps using shims is “shimming.”
Some currently available methods for forming shimming work well when the mated surfaces are both rigid surfaces. The shims formed using these currently available methods may not have the desired level of accuracy when at least one of the mated surfaces is a flexible surface. For example, human operators may take manual measurements of the gaps using feeler gauges. These measurements are then used to determine the dimensions of the shims to be made. However, the very process of taking these measurements, the sequence in which the measurements are taken, or both, may cause changes in the shape of the flexible surface, which may, in turn, cause inaccuracies in the measurements.
Predictive shimming is the process of predicting the shims needed to fill the gaps between mated surfaces and, in particular, predicting the three-dimensional shapes of these shims. Predicting the three-dimensional shapes of these shims includes predicting the overall three-dimensional geometry of the shims. Shims manufactured based on some currently available methods for predictive shimming may be unable to fill these gaps within selected tolerances, fit into these gaps, or both.
For example, a rib assembly for an aircraft wing includes ribs that have shear ties. A wing skin is attached to the ribs such that a flexible surface of the wing skin is mated with a rigid surface comprised of the multiple rigid surfaces of the shear ties. Some currently available methods for predictive shimming include measuring surface geometry using, for example, a laser scanner to generate geometry information. This geometry information is then used to determine the three-dimensional shapes of the gaps that will be present between the mated surfaces.
However, the shape of the flexible surface of the wing skin may change between the time that the wing skin is scanned and the time at which the wing skin is attached to the rib assembly. For example, the wing skin may bend or flex when transported to the location where the wing assembly is to occur, when positioned relative to the rib assembly, when released from the suction cups or other retaining devices used to hold the wing skin, and/or during attachment of the wing skin to the shear ties of the ribs.
Thus, the final shape of the wing skin and thereby, the final shape of the flexible surface of the wing skin that is mated to the surface of the rib assembly, may be different from the shape determined by the scans. Consequently, the gaps may be different in shape and the shims needed to fill these gaps may be different from the shims predicted. The shims may need to be reworked, new shims may need to be made, or both. Performing these types of operations may increase the overall time, cost, and effort needed to manufacture the wing more than desired. Therefore, it would be desirable to have a method and apparatus that take into account at least some of the issues discussed above, as well as other possible issues.